In a semiconductor device manufacturing process, there is known a method for performing a dry cleaning process on a metal film adhered to the inside of a processing chamber of a substrate processing apparatus such as a film forming apparatus or the like. Among metals, a halogenated compound such as Ni (nickel), Co (cobalt), Cu (copper), Ru (ruthenium) or the like has a very low vapor pressure unlike W (tungsten), Ti (titanium), Ta (tantalum) or the like. Therefore, a dry etching employing a conventional etching gas such as ClF3 or the like is performed at a high temperature. As for a method for removing such metal at a low temperature, there is known a method including the steps of: oxidizing a target metal with O2 (oxygen); forming a metal complex by reacting the metal oxide with β-diketone such as hexafluoroacetylacetone (Hhfac) or the like; and sublimating the metal complex to be exhausted (see, e.g., Japanese Patent No. 4049423, and J. Electrochem. Soc., Vol. 142, No. 3, P961 (1995)).
The present inventors have studied the dry cleaning method including the steps of: oxidizing a target metal with O2; forming a metal compound by reacting the oxidized metal with β-diketone such as hexafluoroacetylacetone or the like; and removing the metal compound by sublimation. As a result, the present inventors have found that this method has the following drawbacks.
Specifically, in the above method, the excessive oxidation of the metal leads to abrupt decrease of the reactivity with hexafluoroacetylacetone, so that the etching reaction may be stopped. Therefore, the efficiency of dry cleaning is decreased, or the dry cleaning may not be performed. Such phenomenon is especially prominent when the metal is Ni (nickel).